Posted on 07 Aug, 2014 by James Wykes
When it comes to surface mount production every second counts. That is, of course, if you want to hit your build times and continue to make a profit, which I’m guessing you do, otherwise you wouldn’t be reading this post, right?
The processes involved with printed circuit board assembly (pcba) are complex and numerous, to say the least. Rather than attempt to cover everthing here, let's focus specifically on one of the earlier stages; we consider how the time spent dealing with electronic component packaging issues could be eating away at your profits.
1. Limit the variations in device size
Providing they function correctly within the circuit, it’s not uncommon for a designer to list 2 or 3 similar components on the Bill of Materials (BOM) against the same board reference. This gives the procurement team greater flexibility when sourcing items, which makes perfect sense. However, whilst electrically similar, the parts supplied by different manufacturers can sometimes be physically different in size and shape. As the surface mount pick and place programme will have originally been set up against one part, any deviations outside the tolerances it expects can result in the part being rejected and the line coming to a stop.
It's best practise to settle on just one of the approved parts. Ask whoever is supplying your material to limit the number of times alternatives are supplied. And if they do have tosource a substitute, make sure they make you aware in advance. This way the pick and place programmes can be updated offline which helps you avoid costly machine downtime.
2. Always request taped and reeled over tubed formats
Linked to the above, the format in which devices are supplied, particularly Integrated Circuits (ICs), can vary. Common packaging methods include waffle trays, tubes and reels. Sometimes, it’s simply the case of changing the letter or number at the end of the part number, which makes the difference and changes the format.
For the best efficiency levels the preference is always to receive reeled parts rather than tubed, as the quantity of the devices supplied in a single format is much larger. Tubed components require operators to continually change the parts over, as the tubes become empty – which obviously adds extra time to your manufacturing process and increases the opportunity for operator error, resulting in a tube being fitted in the wrong orientation.
It may not always be possible to receive parts taped and reeled direct from the manufacture. And, on very small batch sizes, like New Product Introductions (NPI) for example, it won’t make commercial sense to buy a larger quantity of device just to get it in a taped and reeled format. It’s important then to try and put a supply chain in place that supports your business and the products that you make.
3. Re-reeling components can save you time on the line… sometimes!
Changing a part from a tubed package to a taped and reel format can increase your efficiency levels - by reducing the time operators have to spend changing parts over during build. Whether you carry out this process yourself, or subcontract it to a third party, it can be done offline which eliminates the impact on production times. However, you need to make sure the quality of the seal on the cover tape is very good and consistent throughout. Poor quality seals can lead to the cover tape coming away which can then cause components to fall from the tape and become damaged or lost.
4) Avoid splicing components together
‘Splicing’ components together is usually only carried out when a number of smaller amounts of taped and reeled components have to be joined together to make one larger, continuous ‘strip’ or quantity. Similar to the re-reeling of devices, if poorly executed, this can result in the tape getting stuck in the surface mount machine feeders. And when the cover tape is pulled away from the carrier tape, the machine can become jammed until the operator resolves the problem.
5) Demand a few more components than you plan to use
As with every manufacturing process, from time to time things won’t go exactly to plan. Despite all efforts to improve packages, your surface mount machine may misplace or drop a component. When faced with a component shortage during smt, your production team usually have two options, neither of which are ideal:
Option 1 - Continue the smt build with the shortage and then fit the part by hand when they arrive. This isn’t favoured as it effects quality results, brings in a risk of damage and quality issues during the rework process, and increases lead times due to re-inspection on AOI equipment.
Option 2 - Hold the job on the line until replacement parts arrive. Not only is this likely to impact your production schedule, your machines will once again be idle at a significant cost to your business.
So if there’s no attrition built into your kit of parts, the device that normally costs you less than a penny, could end up being responsible for several hundreds of pounds of additional rework.
It’s important to continually monitor and refine your pcb assembly processes. And don’t forget to communicate what you really want to those responsible for the material supply. Work closely with those you trust to manage your supply chain, and start to eliminate those online processes that currently keep adding to your costs. And when you start seeing those efficiency graphs getting back to where they should be, why not take a step back. Where else in your organisation can you reduce costs further or increase efficiencies? I bet you find other areas once you start really looking.
Image by Olivia Alcock